Process for quench-hardening steel



Patented June 10, 1952 PROCESS FOR QUENCH-HARDENING STEEL Ernest R. Corneil, Stamford Centre, Ontario, Canada, assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Application August 8, 1950, Serial No. 178,341

Claims. 1

This invention relates to the heat treatment of metals and more particularly to a novel process for quenching.

The physical properties of the various metals used for construction such as iron, copper, nickel, aluminum and their alloys can be modified by various known methods of heat treatment wherein the metal is heated to some definite temperature and then cooled. In many of such heat treating operations, the hot metal is cooled more or less rapidly and such rapid cooling operations are generally known as quenching. Generally, quenching is accomplished by immersing the hot metal in a bath of a liquid such as water or oil. A common quenching operation is the quenching of steel in water or other aqueous liquids or in oil to harden the steel.

Water, which is the cheapest quenching liquid and which produces very rapid cooling, is not suitable for quenching many kinds of steel. In many steel heat treatment operations, the steel is quenched in a hydrocarbon oil which gives a relatively slow rate of cooling, which is required to produce certain desired physical properties such as hardness and ductility. Rapid cooling caused by water quenching in steel hardening operations result in excessive strains in certain kinds of steel which warp and crack the steel. The slower cooling rate afforded by oil quenching prevents such excessive strains but often does not develop maximum hardness. It therefore is desirable to provide quench liquids which will cool the metal at rates intermediate between oil and water quenches, whereby the greatest degree of hardness can be obtained without warping or cracking the steel. Oil quenching is expensive, not only because of the initial cost of the oil but also because the oil deteriorates in use and must be refined or replaced with fresh oil. The inflammable nature of hydrocarbon oils also presents a serious fire hazard in oil quenching operations. The art has long sought for cheap substitutes for oil but without much success. Aqueous solutions of salt or caustic soda, which are used to some extent, provide an even faster rate of cooling than water and are not suitable for use where a cooling rate intermediate between those obtained in water and oil is desired. Various aqueous solutions or dispersions of organic materials such as starch, glue, pectin, natural gums and the like have been from time to time proposed as steel quenching liquids but these have not proved successful as substitutes for quenching oils. 7

An object of the present invention is a new and useful process for quenching metals in heat treating processes. A further object is to'provide novel aqueous liquids to serve as quenching media. Another object is to apply a protective, resinous coating on metal surfaces. Still other objects will be apparent from the following description of the invention.

The above objects may be attained in accordance with the present invention by quenching a metal in an aqueous liquid which contains a vinyl resin.' The quench liquid may be an aqueous solution of a water soluble vinyl resin or an aqueous dispersion of a water insoluble resin. Examples of vinyl resins suitable for practicing the invention are the polymers of vinyl esters of carboxylic acids such as polyvinyl acetate, copolymers of such vinyl esters with other polymerizable materials such as styrene, acrylicesters, acrylonitrile, vinyl halides, maleic anhydride, vinylidene chloride, ethylene and the like. Preferably, one or more polyvinyl esters will comprise at least molar percent of the composition of such copolymers. I may also use as quenching media aqueous dispersions or solutions of polyvinyl alcohols, that is, the complete or partial hydrolysis products of the polyvinyl ester polymers or copolymers. Likewise, I may employ partial polyvinyl alcohol derivatives such as partial aoetals, partial esters or the like wherein part of the hydroxyl groups of the polyvinyl alcohol have been reacted with reagents such as ester forming reagents or acetal forming reagents such as aldehydes, ketones or the like. The various known types of polyvinyl alcohols and polyvinyl alcohol derivatives are well known in the chemical art.

The concentration of the vinyl resin in the aqueous quench liquid will depend upon the nature of the vinyl resin utilized, and the desired rate of cooling in the quenching operation. In most cases, the vinyl resin concentration will lie within therange of 0.1 to 10% by weight. Generally, I prefer to utilize about 0.5 to 3% by weight of the vinyl resin.

By appropriate adjustment of vinyl resin content the cooling characteristics of the quench liquids may be made to substantially duplicate those of the various commonly used quenching oils. Also by increasing the vinyl resin content, c. g., to 3% or higher, the cooling rate of the quenched liquid may be decreased to a lower cooling rate than that of oil. Similarly, by lowering the vinyl resin content, for example, within the range of around 0.1 to 1% by weight, the cooling rate of the liquid may be made faster 3 than that of oil. As the resin concentration is still further decreased, the quenching characteristics of water are approached.

I have found that with the vinyl resin quench solutions of the present invention, I am able to substantially duplicate the results obtained by oil quenching. For example, two identical specimens of a conventional oil hardening steel were quenched, one in a standard quenching oil, and the other in a 1.25% by weight dispersion of polyvinyl acetate in water. quenched by heating it to a temperature of 1530 F. and immersing the hot specimen in the quench liquid until cooled to a temperature of at least 400 F. After cooling, both specimens were found to havea hardness of 62 Rockwell C.

While the quench liquids of the present invention may be utilized for the heat treatment of various kinds of metals and alloys, I believe that the greatest usefulness for the invention is in the heat treatment of various kinds of steel, including alloy steels, and particularly for quenching steel at temperatures within the range of about 700 to 1800 F.

A prime advantage of the quench liquids of my invention is that I can obtain rates of cooling substantially identical with those of commonly used quenching oils, over substantially the entire temperature range of about 700 to 1800 F; For this reason, it is possible with my quench liquid to substantially duplicate the results obtained with the commonly used oil quenches. As the cost of the herein described quench liquids is only a small fraction of the cost of commonly used quenching oils or oil quenches, the utilization of my invention results in a great economic advantage.

My quench liquids also may be used to provide cooling rates intermediate between those of oil and water quenches and thus I can obtain the maximum degree of hardness in certain grades of steel without warping or cracking. A further advantage is the elimination of the fire hazard which accompanies the use of oil quenches.

Another advantage of my invention is that metal parts quenched in the herein described quench liquids at temperatures within the range of about 700 to 1800 F. acquire an adherent resinous film which has excellent corrosion resistant properties. Thus, by quenching steel from around 1500 to 1600 F. in an aqueous polyvinyl acetate dispersion of around 1 to 3% concentration, or in a polyvinyl alcohol solution of Each specimen was the same concentration, the resulting hardened steel acquires a substantially colorless, transparent, adherent resinous film. The film is durable and efiectively protects the hardened steel article from rusting and other forms of corrosion for a long period of time. My process, therefore, may be employed to simultaneously heat treat a metal and provide it with a durable protective coating.

I claim:

1. The process for heat treating steel comprising heating the steel to a quench hardenin temperature and thereafter quenching said steel by immersion in an aqueous liquid containing 0.1 to 10% by weight of a polyvinyl resin.

2. The process according to claim 1 characterized in that the aqueous liquid contains 0.1 to 10% by weight of a vinyl resin selected from the group consisting of polyvinyl esters of carboxylic acids, copolymers of said esters with other polymerizable materials, which copolymers contain at least molar percent of said polyvinyl esters, and hydrolysis products of said polyvinyl esters and copolymers.

3. The process for heat treating steel comprising heating the steel to a quench hardening temperatureand thereafter quenching said steel by immersion in an aqueous liquid containing about 0.5 to 3% by weight of a polyvinyl resin.

4. The process for heat treating steel comprising heating the steel to a quench hardening temperature and thereafter quenching said steel byimmersion in an aqueous liquid containing about 0.5 to 3% by weight of polyvinyl acetate.

5. The process for heat treating steel comprising heating the steel to a quench hardening temperature and thereafter quenching said steel by immersion in an aqueous liquid containing about 0.5 to 3% by weight of polyvinyl alcohol.

ERNEST R. CORNEIL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,215,278 Swartz et al Sept. 17, 1940 2,362,397 Pearce Nov. 7, 1944 OTHER REFERENCES Modern Plastics, June 1947, p. 111, and August 1947, pp. 109-111. 

1. THE PROCESS FOR HEAT TREATING STEEL COMPRISING HEATING THE STEEL TO A QUENCH HARDENING TEMPERATURE AND THEREAFTER QUENCHING SAID STEEL BY IMMERSION IN AN AQUEOUS LIQUID CONTAINING 0.1 TO 10% BY WEIGHT OF A POLYVINYL RESIN. 